Acoustic diaphragm



Jan. 8, 1952 Filed Oct. 20, 1948 A. H. JOHNSON 2, 30

- ACOUSTIC DIAPHRAGM 3 Sheets-Sheet 1 IN VEN TOR.

Jan. 8, 1952 A. H. JOHNSON 2,582,130

ACOUSTIC DIAPHRAGM Filed 001;. 20, 1948 3 Sheets-Sheet 2 o O 0 g 3 m 0CYCLE-5 PER MINUTE- IN V EN TOR.

Jan. 8, 1952 Filed OGt. 20, 1948 A. H. JOHNSON ACOUSTIC DIAPHRAGM 3Sheets-Sheet 5 2% WWW Patented Jan. 8, 1952 ACOUSTIC DIAPHRAGM Arthur H.Johnson, St. Charles, 11]., assignor to Hawley Products Company, St.Charles, 111., a

corporation of Delaware Application October 20, 1948, Serial N 0. 55,592

1 Claim. 1 This invention relates in general to acoustical devices andmore particularly to an improved type of sound reproducing diaphragm.

An unfortunate general characteristic of acoustic diaphragms is the dropin the intensity of sound which occurs at around 1000 to 1200 cycles.The intensity of sound increases beyond that point so that the frequencycurve of a loud speaker diaphragm will show a valley or icicle atbetween 1000 and 2000 cycles. Since the above described drop in soundintensity occurs well within the practical audible range, faithful soundreproduction is seriously hampered. Many attempts have been made toremedy this undesirable inherent characteristic of acoustic diaphragms,but up to this time none has been entirely successful.

It is an object of this invention to provide a sound producer orreproducer which will have a substantially even response curve where allsounds of the practical audible range will be produced or reproducedwith substantially equal efficiency.

Another object of this invention is to provide a diaphragm capable ofreproducing both high and low frequency sounds corresponding inintensity, timbre mellowness, and other qualities with the originallyproduced sound waves.

Another object of this invention is to provide a diaphragm in which theintensity of sound is maintained uniformly high over the greater part ofthe practical audible range.

A still further object of this invention is to provide a diaphragm inwhich the peaks and valleys of sound intensity are smoothed out into amore even response curve.

These and other objects of the invention will become more apparent fromthe following description of the drawings in which:

Fig. 1 represents a rear plan view of the new conical diaphragm, whichis the subject of this invention;

Fig. 2 is a sectional view along the lines 2-2 in Fig. 1 of the newconical diaphragm;

Fig. 3 is a detailed sectional view corresponding to Fig. 2 and showingthe individual components of the new diaphragm;

Fig. 4 shows the frequency response curves for a standard diaphragm andfor the new diaphragm. The curve for the standard diaphragm isrepresented by the heavy line while the curve for the new diaphragm isrepresented by the light line, and

5 is a detailed drawing of the supplemental vibratile part showing theexact curvature and design of the part. The dimensions in this drawingare actual dimensions in inches and the scale of the drawing is eightinches equals one inch.

By the practice of this invention it is now possible to make a soundreproducing diaphragm in which the characteristic drop in soundintensity of standard diaphragms between 1000 and 2000 cycles iseliminated. The new diaphragm, which is the subject of this invention,minimizes the rises and dips in the frequency response curve. The newdiaphragm equalizes vibrations in the diaphragm at frequencies Where thestandard type of diaphragm suffers severe changes in vibration. Hence,by the employment of the new diaphragm, it now becomes possible toreproduce a substantially even response curve throughout the practicalaudible range.

Considering the drawings now in more detail, Fig. 1 represents a rearplan view of a diaphragm prepared according to the present invention.The body of the diaphragm corresponds to the standard type of diaphragmin which I represents a border portion which is adapted to be securedwithin a loud speaker assembly. The vibratile portion 3 is in the shapeusually employed in standard diaphragms. The thin corrugated section 2represents the .undulated portion which is employed in standard speakerdiaphragms to allow maximum freedom of vibration of the vibratileportion without interference from the support. Part 4, as is bestrepresented in Fig. 2, shows the type of construction employed instandard speaker diaphragms for the retention of the voice coil 5. Theportion 4 is in the form of an inverted cone or reentrant having aflange represented at 6 into which the voice coil 5 is inserted. Up tothis point the diaphragm construction corresponds to the ordinarypractice within the industry. The diaphragm may be conical in form, orit may be elliptical or pyramidal as desired.

The frequency response curve for a standard daphragm is represented bythe heavy line on the chart in Fig. i. It will be seen from Fig. 4 thata response curve for a standard type diaphragm reaches a peak of about110 decibels of sound intensity at about 1000 cycles and then rapidlydrops off to about 90 decibels at about 1500 cycles. Such a severe andsharp drop in the intensity of the sound being reproduced by thisdiaphragm results in very unsatisfactory listening qualities. In thepast it has been the practice to attempt to regulate the sound intensityin the above-mentioned range by artificial means, but results have notbeen satisfactory.

According to the present invention, a second vibratile portion of veryspecial design is attached to the vibratile portion 3 of the standarddiaphragm at the point I where the diaphragm is inverted to form areceptacle for the voice coil 5. In Fig. 3 the supplemental portion 8 isseen as composed of a flared or curved outer section 9 which connectsthe overlapping support section In and the flat centerpiece l l. Thedesign of the curved portion 9 must be very carefully controlled asshown in Fig. 5. The supplemental vibratile piece 8 is attached to thestandard cone at the point i by any suitable method such as, forinstance, by gluing the parts together.

The function of the supplemental vibratile part 8, which may be referredto generally as a reentrant member, is that of preventing rises and dipsin the frequency response curve of the standard diaphragm. Hence, thereentrant may be called an antiresonant since its purpose is to beantiresonant when the rest of the system is resonant, and to be resonantwhen the rest of the system is antiresonant. The particular design ofthe reentrant 8 is such that its natural resonant period occurs at thefrequency (1000-2000 cycles) where the response curve of the standarddiaphragm shows a gap or icicle. The light curve in Fig. 4 representsthe frequency response curve of a diaphragm modified according to thepresent invention. It will be seen that the response curve is relativelyflat between 100 and 1500 cycles. Then, instead of dropping from 110decibels to 90 decibels as the standard diaphragm does, the newdiaphragm reproduces sounds smoothly and with steady intensity up toabout 2000 cycles, rising gently to a maximum of about 113 decibels atabout 2200 cycles. Then there is a gradual falling off in intensity toabout 108 decibels at about 3500 cycles, after which the frequency curveof the new diaphragm assumes approximately the same characteristics asthat of the standard diaphragm. Hence, it will be apparent that theintensity of sound reproduced by my new diaphragm does not undergo theusual changes at the center of-the audible range to which ordinarydiaphragms are subject. On the contrary, uniformly high intensity ofsound is produced which carries from the lower limit of the audiblerange up to 3500 cycles on the upper limit of the practical audiblerange.

The shape of the reentrant diaphragm 8 must be carefully controlledaccording to the design shown in Fig. 5. The reentrant member 8 is showntherein as consisting of a neck or centerpiece I l, a curved portion 9and a border Ill. The exact curvature of the portion 9 is indicated bythe reference dimensions under the curve. The

shape is particularly important because the reentrant must vibrate insuch manner as to fill in the frequency response curve at the point(between 1000-2000 cycles) where a standard diaphragm undergoes a lossin intensity. At the same time the supplemental reentrant should beantiresonant duuring the periods when the standard diaphragm isresonant. It has been found that the reentrant 8 must correspond closelyto the design of Fig. 5 in order that the above described results may beobtained. Other shapes and designs of vibratiles have been tried inplace of the design of Fig. 5 but none gives the supplementingvibrations which are required to fill in and extend the frequencyresponse curve of the standard diaphragm. For example, fiat pieces andother designs of diaphragms and caps have been employed withoutsatisfactory results.

The standard diaphragm and the reentrant 8 are preferably made of moldedfibrous material. Any of the commonly known fiber molding methods may beemployed, such as, for instance, the method outlined in U. S. Patent1,984,019, issued to Jesse B. Hawley, December 11, 1934:. By such amethod the parts are made in one single piece and without any seam. Theyare thin and light in weight to reduce to a minimum the mass inertia ormomentum thereof. In the process of molding the fibers are preferablydeposited on a porous former until a blank is made. The blank of substantially uniform thickness throughout is ordinarily compressed whilestill wet or moist to compact the fibers. The blank may then be driedaccording to any of the ordinary methods, and it may be further treatedwith a bonding or waterproofing agent as desired.

It will be apparent from the foregoing disclosure and descriptions thatthe practice of this invention now makes possible the reproduction ofall sounds within the practical audible range without a damaging gain orloss in intensity at a point within said audible range. As a result, aremarkable faithfulness of sound reproduction is accomplished which hasheretofore been impossible to achieve.

The invention is hereby claimed as follows:

An acoustic diaphragm comprising a primary vibratile sound producingmember of general conical diaphragmatic type having a reentrant apicalportion and an auxiliary vibratile reentrant member enclosing the top ofsaid apical portion of said primary member, said auxiliary membercomprising a flat centerpiece and a flared outer section, the curvatureof said outer section corresponding to the curve shown in Fig. 5 of thedrawings.

' ARTHUR H. JOHNSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,512,323 Gersch June 20, 1950FOREIGN PATENTS Number Country Date 435,670 Great Britain Sept. 25, 1935

